Transformation of Bromine Species During Decomposition of Bromate under UV Light from Low Pressure Mercury Vapor Lamps

Bromate decomposition with low pressure mercury vapor lamps (LPMVL) was studied in buffer-free and buffered Milli-Q water by following the fate of bromine species BrO₃ ^?, Br^?, and free bromine. BrO₃ ^? was converted over time to Br^? with total free bromine (TFBr) as secondary reaction product. BrO₃ ^? decay followed pseudo-first-order kinetics and was independent of [BrO₃ ^?]_o (0.06–0.6 mM), pH_o (6.9–9.5) and HCO₃ ^? (0.05–1.0 mM), slightly dependent on acetate (0.06–0.27 mM), highly dependent on and adversely affected by humic acids (HA) and an increasing function of photon flux I as measured by potassium ferrioxalate actinometry. Reaction pH dropped by as much as 2.2 units at pH_o ≤ 8.5 in the buffer-free experiments, while it remained within 0.5 unit at pH_o > 9. TFBr decay due to exposure to LPMVL resulted in formation of Br^? (major) and BrO₃ ^? (minor). Decay of HA in the presence of BrO₃ ^? was highly augmented by photon emission of LPMVL at 185 nm and was found to substantially contribute to BrO₃ ^? decay in the presence of HA. Correlations on the dependency of bromine species decay or formation rates as a function of photon flux are presented.     

Comparison of Low Pressure and Medium Pressure UV Lamps for UV/H2O2 Treatment of Natural Waters Containing Micro Pollutants

UV/H₂O₂ advanced oxidation is an effective barrier against organic micro pollutants. Several studies have focused on the degradation of a wide range of pollutants, but regarding the comparison of low-pressure mercury lamps (LP) with medium-pressure mercury lamps (MP) with respect to energy consumption by the UV/H₂O₂ process, little is known so far. Although the absorbance of H₂O₂ at 254 nm is low, the results of this research show that the yield of hydroxyl radical formation (OH_CT) with LP lamps is comparable or higher than with MP lamps. In a water matrix with a background absorbance due to organics and nitrate, H₂O₂ absorbs UV light very effectively at 254 nm. Generally, due to the contribution of direct photolysis, the degradation of pollutants is better with MP-UV/H₂O₂ than with LP-UV/H₂O₂ at the same UV fluence. Therefore, with LP-UV/H₂O₂ micro pollutants are predominantly degraded through reaction with OH radicals. However, due to the much higher efficiency of LP lamps in converting electrical energy to UV-C light, the energy required to achieve 90% degradation (E_EO) of pesticides and pharmaceuticals can be significantly lower with LP-UV/H₂O₂ than with MP-UV/H₂O₂. Results of bench-scale tests show E_EO data of the LP-UV/H₂O₂ process to be 30%–50% lower than for the MP-UV/H₂O₂ process. At these process conditions MS2 phage inactivation was found to be more than 8 logs for both MP-UV/H₂O₂ and LP-UV/H₂O₂.     

Surface‐initiated atom transfer radical polymerization (ATRP) of styrene from silica nanoparticles under UV irradiation

Diethyldithiocarbamyl‐modified silica nanoparticles were prepared and used as macroinitiator for the surface‐initiated atom transfer radical polymerization (SI‐ATRP) of styrene under UV irradiation. Well‐defined polymer chains were grown from the nanoparticle surfaces to yield particles composed of a silica core and a well‐defined, densely grafted outer PS layer with a mass ratio of styrene to silica, or percentage grafting, of 276.3% after an UV irradiation time of 5 h. Copyright © 2004 Society of Chemical Industry